This invention relates to a linear/rotary actuator, and more particularly to a linear/rotary actuator for actuating a machine or an equipment such as an arm of a robot, a nozzle for a winding machine or the like which carries out both linear motion and rotary motion.
Driving of a machine or an equipment such as, for example, an arm of a robot, a nozzle of a winding machine or the like often requires an actuator which is constructed so as to carry out linear motion and rotary motion not only individually (linear/rotary uniaxial motion) but concurrently (linear/rotary biaxial motion). Actuators for such biaxial motion include two types of actuators. One of them is a linear/rotary actuator of the type that simply an actuator for linear motion and that for rotary motion are combined with each other. More particularly, the actuator is so constructed that a rotary driving motor and a linear driving motor are independently arranged so as to transmit power through a complicated transmission mechanism to a single output shaft to carry out rotary/linear biaxial motion. The other actuator is a linear/rotary actuator of the type that a rotary driving motor and a linear driving motor are linearly arranged so as to directly carry out either rotary driving of an output shaft or linear driving thereof without using any complicated transmission mechanism. The actuator of the latter type is disclosed in, for example, Japanese Patent Application Laid-Open Publication No. 296308/1993, wherein two motors linearly arranged in juxtaposition to each other so as to define an axis of the actuator by cooperation with each other permit a single output shaft to carry out linear/rotary biaxial motion. Both former and latter linear/rotary actuators are disclosed in Japanese Patent,Application Laid-Open Publication No. 292343/1994.
The linear/rotary actuator disclosed in Japanese Patent Application Laid-Open Publication No. 292343/1994 is constructed in such a manner that a single output shaft is formed with both a ball screw and a spline. The ball screw and spline are driven either through a transmission mechanism or directly by means of both a rotary driving motor and a linear driving motor. Unfortunately, such construction of the linear/rotary actuator disclosed causes a problem that the output shaft carries out linear motion with rotation of a rotor of the rotary driving motor when a rotor of the linear driving motor is kept interrupted during rotary motion. In order to solve the problem, it is required to control the linear driving motor in coordination with the rotary driving motor during rotation thereof. This renders control of both rotary and linear driving motors highly troublesome and complicated and leads to both a failure in control and misregistration in control.
Also, the above-described latter linear/rotary actuator disclosed in Japanese Patent Application Laid-Open Publication No. 296308/1993 is so constructed that the single output shaft described above is adapted to carry out both rotary motion and linear motion and formed with a ball screw and a spline. The ball screw is threadedly engaged with a nut driven for rotation through the linear driving motor and the spline is linearly movably fitted in a groove of a shaft driven for rotation through the rotary driving motor. Driving of the linear driving motor rotates the nut, leading to linear motion of the output shaft, whereas driving of the rotary driving motor leads to rotation of the output shaft through the shaft. Such construction of the linear/rotary actuator permits it to be relatively simplified in structure and reduced in whole size. However, the linear/rotary actuator causes linear motion and rotary motion to be mechanically synchronized with each other, to thereby fail to individually carry out linear motion and rotary motion. For example, it fails in execution of only rotary motion, because the ball screw is rotated relatively to the nut, to thereby fail to rotate the output shaft while holding it against linear motion. Likewise, it fails to concurrently carry out both linear motion and rotary motion because it ensures linear motion in only one direction but causes a reduction in speed of linear motion in the other direction or fails in linear motion in the other direction. Such a restriction fails to permit the linear/rotary actuator to satisfactorily exhibit general-purpose properties.
In addition, the conventional linear/rotary actuator fails to optionally and positively carry out linear motion and rotary motion, leading to a failure to permit so-called box motion (linear motion, rotation, linear motion and rotation) as required in operation of a nozzle of a winding machine to be repeatedly executed at an increased speed.
The present invention has been made in view of the foregoing disadvantage of the prior art.
Accordingly, it is an object of the present invention to provide. a linear/rotary actuator which is capable of simply and positively attaining linear motion and rotary motion either concurrently or individually while arranging a rotary driving motor and a linear driving motor in a manner to be coaxial with each other.
It is another object of the present invention to provide a linear/rotary actuator which is capable of being constructed into a simplified and compact structure.
The present invention relates to an improvement in a linear/rotary actuator including a linear motor which is described in U.S. Pat. No. 6,081,051 (U.S. Ser. No. 09/212,030) assigned to the assignee, the disclosure of which is hereby incorporated by reference herein. Thus, in accordance with the present invention, a linear/rotary actuator is provided. The linear/rotary actuator includes a linear motor including a hollow linear shaft acting as a movable element and an output shaft formed on forward and rearward portions thereof with forward and rearward spline sections each having a predetermined length, respectively. The output shaft has an intermediate portion on which the forward and rearward spline sections are not formed. The intermediate portion of the output shaft is rotatably inserted through the linear shaft by means of an intermediate bearing structure. The linear/rotary actuator also includes a nut fitted on the forward spline section of the output shaft, a rotary driving motor for rotating the nut either directly or through a transmission mechanism, to thereby rotate the output shaft, and a rearward bearing structure including a fixed section having the rearward spline section fixed thereto. The rearward bearing structure supports the rearward spline section so as to permit sliding of the rearward spline section in an axial direction of the actuator and rotation of the output shaft. Arrangement of the rearward bearing structure permits the output shaft to be supported in a dual-support manner, to thereby significantly reduce generation of vibration. In order to rotate the output shaft through driving of the rotary driving motor, the output shaft is provided thereon with the front and rear spline sections and the nut fitted on the forward spline section is directly rotated, so that the output shaft may be rotated through the rotary driving motor. Alternatively, the nut may be rotated through a transmission mechanism to drive the output shaft through the rotary driving motor.
The term xe2x80x9cspline sectionxe2x80x9d referred to herein means a mechanism or structure which permits movement of a shaft in an axial direction thereof. The forward spline section described above is fitted thereon with a nut called a spline nut. The forward spline section keeps the shaft from being rotated when the spline nut is kept locked or fixed. When the nut is rotated due to application of force for rotation thereto while being kept unfixed, the forward spline section functions to transmit the force to the shaft. The rearward spline section formed on a rearward portion of the output shaft does not have any nut for transmission of force for rotation fitted thereon. The rearward spline section is fixed to the fixed section of the linear/rotary actuator and supported on the rearward bearing structure which permits sliding of the rearward spline section in the axial direction and rotation of the output shaft. The forward spline section and rearward spline section each may be configured in the form of either a groove or a projection which extends in the axial direction. The nut fitted on the forward spline section is engaged with the forward spline section, so that rotation thereof around the shaft may be prevented.
In accordance with this aspect of the present invention, a linear/rotary actuator is provided. The linear/rotary actuator includes a linear motor including a stator fixed on a frame and a hollow linear shaft acting as a movable element and an output shaft formed on forward and rearward portions thereof with forward and rearward spline sections each having a predetermined length, respectively. The output shaft has an intermediate portion on which the forward and rearward spline sections are not formed. The intermediate portion of the output shaft is rotatably inserted through the linear shaft by means of an intermediate bearing structure. The linear/rotary actuator also includes a nut fitted on the forward spline section of the output shaft and constructed so as to permit sliding of the forward spline section in an axial direction of the actuator; a rotary driving motor including a revolving shaft configured into a hollow structure and having the nut fixed therein, a rotor fixed on said revolving shaft and a stator fixed on said frame; a forward bearing structure for rotatably supporting the revolving shaft on the frame; and a rearward bearing structure including a fixed section fixed on the frame, an outer ring fixed on the fixed section and an inner ring fitted on the rearward spline section so as to permit sliding of the rearward spline section in the axial direction.
The linear driving motor for driving the linear shaft is constituted by a linear motor and directly uses the linear shaft as a movable element for the linear motor. Any suitable motor may be used as the rotary driving motor. However, a servomotor or a step motor may be suitably used in order to enhance controllability of the linear driving motor. When the linear motor is used for this purpose, the revolving shaft of the rotary driving motor is configured into a hollow structure, the linear shaft is constituted by the movable element of the linear motor, and the linear shaft is formed into a length which permits it to extend through a central portion of the revolving shaft of the rotary driving motor so that the output shaft may be arranged in a manner to be rotatable with respect to the linear shaft. The revolving shaft of the rotary driving motor has the nut fixed thereon and fitted on the forward spline section provided on the output shaft.
In the present invention, as described above, the linear motor is used as the linear driving motor, to thereby directly drive the linear shaft without any spline means or threaded means, resulting in the linear/rotary actuator being highly simplified in structure. In particular, when the linear motor which includes the hollow linear shaft acting as the movable element is used and the output shaft is rotatably inserted through the linear shaft by means of the intermediate bearing structure, the linear/rotary actuator of the present invention may be configured in a compact manner.
Also, the linear/rotary actuator of the present invention may include at least one detent mechanism arranged between the linear shaft of the linear motor and the fixed section so as to prevent rotation of the linear shaft about the output shaft. This effectively reduces generation of vibration from the linear shaft. A plurality of such detent mechanisms may be arranged so as to be spaced from each other at equal intervals in a direction of rotation of the output shaft.
The rearward bearing structure may be fixed to the fixed section arranged on a rearward side of the linear shaft. In this instance, the detent mechanism may include an elongated bar-like member fixed to the linear shaft so as to rearwardly extend therefrom and a guide member provided on the fixed section and fitted on the bar-like member. The guide member may be configured to permit sliding of the bar-like member in the axial direction but prevent rotation of the bar-like member about the output shaft.
The linear/rotary actuator may further include a position sensor for detecting a position of a rearward end of the bar-like member. This facilitates detection of a position of an origin of the output shaft, to thereby facilitate positional control of the output shaft in a direction of linear motion thereof.
In order to more forwardly arrange the rear bearing structure, the linear/rotary actuator of the present invention may be constructed in such a manner that the fixed section may be constituted by a fixed section body arranged on the rearward portion of the linear shaft and a cylindrical member fixed at a rearward portion thereof to the fixed section body and arranged concentrically with the linear shaft and output shaft so as to forwardly extend between the linear shaft and the output shaft, the rearward bearing structure is fixed on a forward end of the cylindrical member, and the detent mechanism includes an elongated bar-like member fixed to the fixed section body so as to forwardly extend therefrom and a guide member provided on the linear shaft and fitted on the bar-like member, wherein the guide member is configured to permit sliding of the linear shaft in the axial direction but prevent rotation of the linear shaft about the output shaft. Also, the cylindrical member may be formed into a length which permits the intermediate bearing structure and rearward bearing structure to be arranged in proximity to each other. Such configuration reduces a distance between the intermediate bearing structure and the rearward bearing structure and permits the rearward bearing structure to be arranged in the linear shaft, resulting in a length of the output shaft being decreased, so that the linear/rotary actuator may be significantly reduced in whole length and constructed in a compact manner.
The above-described construction of the linear/rotary actuator of the present invention not only permits linear motion of the linear shaft in the axial direction upon driving of the linear motor, but permits the output shaft to carry out linear motion with the that of the linear shaft. The output shaft is inserted through the linear shaft by means of the intermediate bearing structure, so that rotation of the output shaft does not lead to rotation of the linear shaft. Whereas, when the rotary driving motor is driven to rotate the output shaft, the output shaft may carry out linear motion while carrying out rotary motion because the nut provided in the revolving shaft of the rotary driving motor is fitted on the spline section of the output shaft. The linear shaft may be constructed into a hollow structure and the output shaft may have an intermediate portion on which the forward and rearward spline sections are not formed, so that the intermediate portion of the output shaft may be rotatably inserted through the linear shaft by means of the intermediate bearing structure. In other words, the output shaft is rotatably inserted through the linear shaft by means of the intermediate bearing structure while being concentric with the linear shaft. Such construction permits linear motion of the output shaft with that of the linear shaft but prevents rotation of the linear shaft irrespective of rotation of the output shaft. This permits rotation of only the output shaft at a predetermined position and control of rotation of the output shaft in asynchronism with the linear motion, so that the linear/rotary actuator may exhibit excellent general-purpose properties and be simplified in structure. Synchronism between the linear motion and the rotary motion may be attained by rendering both motions electrically synchronous with each other depending on outputs of rotation detectors or encoders mounted on the linear driving motor and rotary driving motor, respectively.
The rotary driving motor may be constructed so as to rotate the nut fitted on the spline section provided on the output shaft through a transmission mechanism such as a reduction mechanism or the like, to thereby rotate the output shaft.
Further, in accordance with this aspect of the present invention, a linear/rotary actuator is provided. The linear/rotary actuator includes a linear motor including a stator fixed on a frame and a hollow linear shaft acting as a movable element and an output shaft formed on forward and rearward portions thereof with forward and rearward spline sections each having a predetermined length, respectively. The output shaft has an intermediate portion on which the forward and rearward spline sections are not formed. The intermediate portion of the output shaft is rotatably inserted through the linear shaft by means of an intermediate bearing structure. The linear/rotary actuator also includes a nut fitted on the forward spline section of the output shaft and constructed so as to permit sliding of the forward spline section in an axial direction of the actuator; a rotary driving motor including a revolving shaft configured into a hollow structure and having the output shaft inserted therethrough, a rotor fixed on the revolving shaft and a stator fixed on the frame; a reduction mechanism arranged between the revolving shaft and the nut to transmit rotation of the revolving shaft to the nut while reducing a speed of rotation of the revolving shaft; a forward bearing structure for rotatably supporting the revolving shaft on the frame; and a rearward bearing structure including a fixed section fixed on the frame, an outer ring fixed on the fixed section and an inner ring fitted on the rearward spline section so as to permit sliding of the rearward spline section in the axial direction. The reduction mechanism may be constituted by an epicyclic gear mechanism including a rotator, which includes a central gear provided on the revolving shaft and epicyclic gears fixed on the rotator so as to be rotated about the central gear. The rotator may be coupled to the nut and rotatably supported on the frame through a bearing structure. Arrangement of the thus-constructed reduction mechanism facilitates control of rotary motion of the linear/ rotary actuator and permits the actuator to positively carry out rotary motion at high torque even when a miniature motor is used.
The linear/rotary actuator may also include an electromagnetic brake mechanism including exciting coils and arranged between the rotary driving motor and the reduction mechanism. The electromagnetic brake mechanism carries out non-braking operation when the exciting coils are kept excited and braking operation when the exciting coils are kept non-excited. The exciting coils are rendered non-excited when feeding of electricity to the rotary driving motor is interrupted. Arrangement of the electromagnetic brake mechanism permits the brake mechanism to carry out operation when feeding to the rotary driving motor is kept interrupted, to thereby prevent occurrence of any accident due to rotation of the output shaft during non-excitation of the exciting coils. Further, the linear/rotary actuator of the present invention may further include a spring mechanism for constantly applying, to the output shaft, force which rearwardly moves the output shaft. The spring mechanism upwardly pushes the output shaft, to thereby prevent occurrence of an accident due to excessive lowering of the output shaft, even when a power failure occurs in the case that the actuator is operated while keeping the output shaft downwardly extending.